Autofocus should have been improved and is slow. Not great for sports.
Cannot access custom flash functions in camera for the older 580 EX flash. No pop up flash.
Should have continuous autofocus for video.

Great camera and a real step up for most users.
Amazing low light pictures.

Resolution and picture quality are fantastic.

However, the auto focus is really lagging behind the competitors (nikon).

Video mode on this camera is not for the casual user and the lack of continuous autofocus is a killer when you want to film your kids who move all over the place. Newer SLR's coming out will surely have this enabled.

Lack of pop up flash is disappointing for those times you need a quick fill flash or don't want to carry around a giant external flash.